1. Field of the Invention
The present invention relates to the field of water well refurbishing, and more specifically to cleaning devices and techniques for use in cleaning the slots, perforations or other openings present in water well casings or screens.
2. Description of the Prior Art
In most rural environments, water wells are a given necessity. Water wells and their associated down hole pumps are the modern day equivalent of windmills, which were historically used to move water from one location or one depth to another. In addition to providing water for such everyday activities as showering, doing laundry and running the dishwasher, water wells are also used at the present time for such diverse purposes as irrigating crops, providing livestock with water, supplying water to remote locations, or for acting as heating and cooling mechanisms for geothermal systems. The completed water well may utilize any of several commercially available pumps to bring the water to the well surface. For example, three of the commonly used well pumps at the present time are the electric submersible pump, the reciprocating plunger well pump, and the line-shaft turbine pump.
In the present day water well producing arts, it is customary to complete the well by inserting a metallic well liner, sometimes referred to as a “casing”, adjacent the water-producing formation. Water wells throughout the Ogallala aquifer and many other aquifers are cased with steel pipe, typically pipe which is from twelve to sixteen inches in diameter. This pipe is normally perforated by torch cutting or is provided with manufactured slots. Another frequently encountered water well installation uses a screen type pipe, commonly known as “ag screen” or “Johnson well screen.” The purpose of the slots, perforations or screens is to allow the water from the surrounding water bearing formation to infiltrate the casing, while holding back sand or other particulates, so that the downhole pump in the well can transport the water from the water bearing strata to the surface for distribution in irrigation, industrial or consumptive use.
The openings in the well casing thus provide passage-ways for the flow of water and other formation fluids from the formation into the well for removal to the surface. However, over time, the openings will often become plugged with foreign material, such as sand, the products of corrosion, sediment deposits and other inorganic or organic complexes. Over time, these various foreign materials begin to cake up and clog the holes or perforations in the casing or screen. Also, over time, depending upon conditions, lime contained in the water will accumulate around the screen and will also plug up the openings. As the sand, limestone and other materials build or cake up, they close off portions of the perforated casing or screen. This naturally reduces pumping efficiency, reduces intake of water, increases the pumping head, and increases the pumping cost.
Obviously, the smaller the perforations or screen, the more likely the plugging will be and the more quickly the plugging will take place. Mill slot casing and ag screen casing have the smallest openings and are the most likely to plug. Similarly, the smaller torch cut perforations are highly likely to plug, as well. Torch cut perforations range from about ⅛ inch to about ½ inch, depending on the formation in which the well may be drilled. Smaller perforations are typically used to limit sand inflow to the pump.
Since removal and replacement of the well casing is costly, various methods have been developed to clean plugged openings though various remedial operations, including chemical treatments, mechanical techniques (e.g., brushing and bailing), the use of a high pressure air gun to create a hydraulic wave, the use of jetted streams of liquid, re-perforating the casing, etc. In fact, it is often necessary to perform some type of cleaning operation every 2 or 3 years in large municipal or industrial water wells.
The use of fluid jet techniques was first introduced in about 1938 to directionally deliver acid to dissolve carbonate deposits. In about 1958 the development of tungsten carbide jets permitted including abrasive material in a liquid which improved the ability of a fluid jet to do useful work. However, the inclusion of abrasive material in a jet stream was found to be an ineffective perforation cleaning method in that it enlarged the perforation which hampered or destroyed the perforation sand screening capabilities. Other liner and casing cleaning technologies have been described in the prior art in relation to cleaning the liners or casings of oil and gas hydrocarbon producing wells. While there are some similarities to the cleaning of water wells, the oil and gas well rehabilitation equipment tends to be more complicated and expensive with the tools often being run on metal tubing or drill string or off reels of metallic coiled tubing and the like.
With respect to the other prior art processes which have been employed for water wells, none have proved to be entirely satisfactory. Often the surface of the well casing is cleaned relatively well, but the perforations are almost never cleaned out entirely satisfactorily.
A need exists, therefore, for an improved water well cleaning apparatus and method which meets the above noted needs and overcomes the difficulties of the prior art.